Hollow fiber devices are used extensively in separation of fluids both gases and liquids, in mass transfer applications such as adding or removing a gas to or from a liquid that involve transfer of the gas through a membrane and more recently in heat transfer applications.
Heat exchangers built from plastic materials can be light weight and compact while maintaining good heat transfer efficiency. In addition, polymeric heat exchange devices generally are corrosion resistant and can be less susceptible to fouling. The heat transfer efficiency of polymeric materials in heat exchangers can be enhanced by incorporation of inorganic materials with high heat transfer coefficients such as carbon or graphite particles as described in U.S. Pat. No. 6,465,561. It is also known to employ composite heat exchange devices comprised of polymeric materials and metals as disclosed in U.S. Pat. No. 6,742,576.
Heat exchange devices constructed from plastic/polymeric compositions can be divided into planar and tubular configurations. Heat exchange devices of the planar configuration are disclosed in U.S. Pat. Nos. 4,955,435; 5,499,676; 6,336,987 and 6,832,648. Heat exchange devices of the tubular configuration are disclosed in U.S. Pat. Nos. 5,469,915; 6,094,816; 6,302,197, 6,364,008 and US Patent Application Publication US2007/0107884 A1.
A planar arrangement of a device designed for an air to air heat and moisture exchanger is disclosed in U.S. Pat. No. 6,145,588. The device is constructed from composite polymeric membranes that enable the simultaneous transfer of heat and water vapors.
Hollow fibers membrane devices typically have a tubular configuration. Their design is sometimes classified as a bore side feed or a shell side feed device. Examples are disclosed in U.S. Pat. Nos. 3,422,008; 3,690,465; 3,755,034; 4,061,574; 4,080,296; 4,929,259; 5,013,437; 5,837,033; 6,740,140 and 6,814,780. Traditionally, hollow fiber devices have been used as mass transfer devices in the separation of fluid mixtures. Hollow fiber membranes are employed in fluid separation applications such as reverse osmosis, ultrafiltration, and gas separation processes as well as in gas transfer application from and into liquids. Common gas separation applications include generation of nitrogen from air, hydrogen recovery in refinery and petrochemical plants, dehydration of gases and removal of acid gases from the natural gas. The most common gas mass transfer application is removal of dissolved gases from liquids.
An integral component of most if not all existing hollow fiber devices is a tubesheet. Tubesheets are designed to provide a fluid tight seal between the shell side and the bore side of the hollow fiber device. A breach in the tubesheet integrity will compromise the operation of the device.
In existing hollow fiber device tubesheets, the fluid communication with the bore side of the hollow fibers is substantially in an axial orientation. In these arrangements, the hollow fibers are encapsulated in a suitable sealing material to form a terminal tubesheet that is severed to provide fluid access to hollow fiber bores. The direction of fluid thrust through the tubesheets and into hollow fiber bores is axial, i.e. in a direction parallel with the long axis of the hollow fiber device. Examples of conventional tubesheet designs, configured for gas separation assemblies, are shown in FIGS. 2A and 3A-3D of U.S. patent application Ser. No. 13/411,548, filed on Mar. 3, 2012, with the title Fluid Separation Assembly and Method, and U.S. Provisional Application No. 61/494,867, with the same title, filed on Jun. 8, 2011, the contents of both being incorporated herein by reference in their entirety.
Generally, tubesheets are formed from curable resinous materials such as epoxies or polyurethanes or from thermoplastic materials such as polyethylene or polypropylene. Existing tubesheets are often subject to deformation or creep under mechanical load and this limits the useful life of the device. During operation of the hollow fiber device a pressure differential may exist between the bore side of the hollow fiber device and the shell side of the device. In conventional designs, the differential pressure generates loads on the tubesheet that can lead to tubesheet rapture or tubesheet deformation due to creep. The problem is further exacerbated at high operating temperatures, since elevated temperatures often decrease the tensile strength of the tubesheet material promoting tubesheet failures. Since high temperatures and/or high differential pressures between the bore side and the shell side of the hollow fiber device are found to promote tubesheet failure in devices with conventional tubesheet designs such tubesheets often are problematic or entirely unsuitable for use in heat transfer equipment, in mass transfer devices and in fluid separation assemblies.
A number of solutions have been proposed in the art to remedy tubesheet failure under differential load. For example, Semmere et al. in U.S. Pat. No. 7,717,983 describe an air separation module with a load carrying central tube. The design provides for support of tubesheets in bore side feed air separation operation wherein differential pressure exists between the bore side and the shell side of the hollow fiber device.